1. Field of the Invention
The present invention relates to a RAID subsystem, and more particularly, to a coherence preservation method of duplicated data in RAID subsystem.
2. Background of the Related Art
Generally, RAID (redundant array of inexpensive disks) subsystems provide storage management with the effectiveness by recognizing several physical devices as one logical device, and support a characteristic of high availability allowing high performance data input/output and failure in accordance with RAID levels (RAID0 to RAID9).
The RAID subsystem supports several levels of RAID, duplicating and storing the data at a disk array consisting of a number of disk drives, and implements the input/output in parallel. In addition, the subsystem requires a method capable of supporting the availability of the data without not interrupting the service of the system when the error occurs in each RAID level, and rapidly recovering an error data.
For example, RAID1 of a disk mirroring type corresponding to a level 1 of the RAID is any one level of RAID in that the same data is duplicated and stored in different several number of disks to improve the availability and reliability of the data, and the load balancing is implemented from the duplicated data of several disk with respect to the write operation. Temporary and permanent errors generated in the existing RAID subsystem supporting the RIAD1 cause a problem of coherence in the duplicated data.
In particular, the temporary error is generated when access to the disk is not allowed temporally due to several situations, thereby resulting in a problem of data coherence or inconsistency among the disks. The permanent error is generated from a physical failure of the disk, so that it is inevitable to replace the disk and to recover the entire data of the disk in which the error occurs.
Accordingly, the conventional RAID subsystem supporting the RAID1 has to consider a method of preventing the data failure due to the error and of managing the coherence among the duplicated data to maintain the data properly. In order to solve the problem, it has been a method of preventing the data failure from the error by comparing the contents stored in the respective cache to coincide with each other by use of two RAID controllers, thereby securing the correction of the data, and implementing the write on the disk from the cache of the controller used when the error occurs.
Proposed is another method for maintaining the coherence among the duplicated data of the RAID1 in which busy/stale bit used in Petal of virtual disk system is adopted.
According to a method for maintaining the data coherence in the Petal, if the write operation on the data is requested, a busy bit is set to xe2x80x9c1xe2x80x9d before the operation. If the write operation on the entire disks consisting the RAID1 is normally completed, a busy nit is set to xe2x80x9c0xe2x80x9d . If an error occurs in an arbitrary disk, a stale bit is set to xe2x80x9c1xe2x80x9d with respect to a data block to be used from now on. The set stale bit is used upon implementing the temporary error recovery of the disk, and selection recovery is performed with respect to the data blocks with xe2x80x9c1xe2x80x9d of the stale bit.
The Petal method needs the operation expense with respect to the bit every operation, and requires a separate stable disk for the busy/stale bit.
In addition, in order to maintain the data coherence and secure the correction of the data, a method of reading the contents of the respective disk and comparing the contents fo the duplicated data is simple, it provides a drawback of increasing load of the system.
Accordingly, the present invention is directed to a coherence preservation method of duplicated data in RAID subsystem that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to a coherence preservation method of duplicated data in RAID subsystem, in which when an error occurs in disks of the RAID subsystem supporting RAID1 of disk mirroring type, a bitmap managing the information of data coherence (called as FBB (failed block bitmap)) is added, so that it secures the coherence of the duplicated data and supports rapid recovery of the data having improper coherence from a temporary or permanent error, and which when recovering the data due to the permanent error of an arbitrary disk, it is possible to disperse the load on a write operation, and to decrease the recovery expense.
To achieve the object and other advantages, according to one aspect of the present invention, there is provided a coherence preservation method of duplicated data in RAID subsystem, the method comprising the steps of: if a read operation is requested by the RAID subsystem, selecting an arbitrary target disk among disks having duplicated data, and implementing the read operation on the selected disk; implementing a read error handling to determine whether an error occurs in the disks selected upon the read operation, and if the error occurs in the read operation of the selected target disk, repeating the read error handling until the read operation of the data succeeds by circulating the remaining metering-treated disks in turns; after the read error handling, if the read operation on the remaining disk in all succeeds, completing the read error handling, and if the read operation on the remaining disk in all fails, returning the error to the disk, and completing the read error handling; if a write operation is requested by the RAID subsystem, implementing the write operation on the disks having duplicated data; after implementing the write operation, if a temporary error occurs in the duplicated data, implementing a temporary error handling to maintain the data coherence in the disks having the duplicated data and to recover the temporary error; and after implementing the write operation, if a permanent error occurs in the duplicated data, implementing a permanent error handling to maintain the data coherence in the disks having the duplicated data and to recover the permanent error.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.